1. Field of the Invention
The present invention relates to a remote control device for vehicles, and more particularly to a vehicular remote control device for checking a code based on communications with a remote controller and controlling operation of vehicle-mounted devices based on the checking results. More specifically, the present invention relates to a vehicular remote control device suitable for use as a vehicle door lock remote control device.
2. Description of the Related Art
Heretofore, it has been necessary to occasionally diagnose the failure of a vehicular remote control device which controls vehicle-mounted devices. Such a vehicular remote control device is basically made up of a vehicle-mounted unit and a portable unit.
If a conventional vehicular remote control device comprises a vehicle door lock control device, then it is diagnosed for failures according to the following process: When the vehicle door lock control device is normal, the portable unit is in contact with a loop antenna mounted on a vehicle body, and radiates a radio wave which is received by the loop antenna. A reference value Rs which corresponds to the intensity of the radio wave that is detected by the loop antenna is predetermined. The reference value Rs is stored in a memory of the vehicle-mounted unit.
When an ignition key is pulled out of the ignition key cylinder in the vehicle, the vehicle-mounted unit sends a request signal to the portable unit. In response to the request signal, the portable unit sends a key code signal to the vehicle-mounted unit. At this time, the vehicle-mounted unit measures the received intensity Rf of the key code signal sent from the portable unit.
When the vehicle-mounted unit detects that a key code sent from the portable unit and a key code stored in the memory of the vehicle-mounted unit agree with each other, then the vehicle-mounted unit performs a door locking/unlocking process. In other words, the vehicle-mounted unit unlocks the vehicle doors if the vehicle doors are locked, or locks the vehicle doors if the vehicle doors are unlocked. Then, the vehicle-mounted unit checks if the received intensity Rf is greater than or equal to the reference value Rs. If the received intensity Rf is greater than or equal to the reference value Rs, then the vehicle-mounted unit judges that the vehicle door lock control device is normal. If not, then the vehicle-mounted unit judges that the vehicle door lock control device is malfunctioning.
When the vehicle-mounted unit sends a request signal to the portable unit while the portable unit is in contact with the loop antenna, if the vehicle-mounted unit does not detect the condition that the received intensity Rf is greater than or equal to the reference value Rs, then the portable unit judges the possibility of a failure of its own antenna, or the generation of an abnormal carrier frequency, or deterioration of its power supply voltage. Alternatively, the vehicle-mounted unit judges that the loop antenna on the vehicle body may possibly be malfunctioning. See Japanese patent publication No. 5-2791, for example, for details.
Another failure diagnosis process for the conventional vehicular remote control device will be described below. When the failure diagnosis routine starts, the vehicle-mounted unit sends a request signal from a transmission antenna that is positioned near the grip handle of a door on the side of the driver's seat. In response to the request signal from the vehicle-mounted unit, the portable unit sends a radio-frequency return signal to the vehicle-mounted unit. The vehicle-mounted unit receives the return signal with a reception antenna, demodulates the return signal, determines whether a code contained in the return signal and a code stored in the memory of the vehicle-mounted unit agree with each other, and produces a response sound from a buzzer of the vehicle-mounted unit when the codes agree with each other. Then, the user presses a door unlock switch on the portable unit to send a code corresponding to the unlocking of the door from the portable unit. The code is received by the reception antenna of the vehicle-mounted unit, which demodulates the code. When the code is demodulated, the vehicle-mounted unit sends a request signal from another antenna, e.g., a transmission antenna that is positioned near the grip handle of a door on the side of the assistant driver's seat, after which the above process is carried out. While the above request signals are being repeatedly transmitted, the user places the portable unit within the detection range of the transmission antennas, i.e., the range in which the portable unit can receive signals with its reception antenna. This is to confirm a response sound for thereby determining whether the portable unit itself suffers a failure, the transmission antenna and transmitter of the portable unit or the vehicle-mounted unit are malfunctioning, or the reception antenna and receiver of the portable unit or the vehicle-mounted unit are malfunctioning. Reference should be made to Japanese laid-open patent publication No. 2000-85532, for example, for details.
The conventional vehicular remote control device is problematic in that since the portable unit needs to have its transmitter and receiver circuits kept in operation even during the failure diagnosis, the portable unit requires large power consumption in transmitting and receiving radio waves. Incidentally, the portable unit consumes more power when transmitting radio waves than when receiving radio waves, and because the portable unit is battery-powered, the life of its battery and therefore the life of the portable unit itself is shortened.
Another problem of the conventional vehicular remote control device is that the failure diagnosis can detect a malfunction, but it may be difficult to specify the location where the malfunction has occurred.
If the failure diagnosis is carried out on the basis of comparing the level of received signals, then the results of the failure diagnosis may not necessarily be accurate due to noise added to the signals.